Abadom
A DxD fanfic of yours would be a great job (if you followed the line of reason, and not those abominations of putting powers like System in easy mode, people are completely uncreative in Power/World Building, only a few fanfics can be saved, and They are precisely those who avoid this). But it's indisputable that DxD has a lot of room to make great fanfics, just avoiding the idea of a harem with anyone already puts it in the top 10. I also believe that you can work with Jujutsu Kaisen (at least get power ideas like you did with the plasmids in Danmachi, the versatility/complexity makes the Jujutsu Kaisen power system great to work with, even more so because everything considered broken like Mahoraga's power, domain expansion, limitless and others, always have gaps that can be exploited)
In my ranking the Harry Potter fic is first because it has lots of potential if he can even travel on time to other epochs (meet with Merlin, etc), second is the martial arts fic, my only concern is the world jumping because it's normal in those types to not write in depths each world and end up being kinda bland, and DXD fic is last just because I had read lots of them and can't see how it would go to be something new? I guess, and the others ideas some of them looks really interesting.
I also have a idea of fan fiction about attack on titans mc got reincarnation in the world of attack on titans without any knowledge about this world, being born in a nobel house within the inner walls he has a good life compair to normal peoples, but he was not happy, having a desire to explore the outer world and mystery surrounding titans but his parent don't allow him to join the military but one day our mc who was wondering in the town gets kidnapped my human traffickers they plain to sold him in black market for his looks but everything changed when I also have a idea of fan fiction about attack on titans mc got reincarnation in the world of attack on titans without any knowledge about this world, being born in a nobel house within the inner walls he has a good life compair to normal peoples, but he was not happy, having a desire to explore the outer world and mystery surrounding titans but his parent don't allow him to join the military but one day our mc who was wondering in the town gets kidnapped my human traffickers they plain to sold him in black market for his looks but everything changed when our mc got bitten by a strange small insect which was only a centimeter in size while gaining superhuman strength, reflexes, and a seventh sense in the process. mc art
I want to give idea about your three ideas but i honestly haven't watch them yet so although it might be selfish of me but i want to suggest another fanfictions like attack on titans, black clover, douluo dalu 2,3, or 4,hunter hunter, sword art online ya i know I have only given name of the fictions not an actual idea let me think for some time
Have you thought about making a honkai impac fic? Where the MC ends up in the game as an orphan with no relevance and acquires some power that allows him to hide and/or be invisible (How he chose it is up to your imagination). The other one that occurs to me would be from the Nasuverse from there nothing more. Regarding the ideas you wrote, the MC of Harry Potter maybe you could give importance with his knowledge of the modern era (I don't remember what era you mentioned in which the MC was before traveling in time or another world) such as science, chemistry or physics, so you can create your own original spells with your knowledge with their difficulty of course. About high school DxD I don't know what to tell you, I'm on the same page as you